Multilayer molded element

ABSTRACT

A multilayer molded element ( 1 ) is molded to an appropriate shape which conforms to an underside of floor areas or wheel housings of a vehicle. The multilayer structure includes a non-woven, resilient layer ( 3 ) which functions as a shock absorber and spring to absorb impact and damp noise. The resilient layer is disposed between cover layers ( 4, 5 ). Optionally, fabric layers ( 6, 7 ) are bonded to outsides of the cover layers.

[0001] The invention relates to a multilayer molded element suitable forbottom covering of vehicle floor areas or wheel housings. Moldedelements of this type are utilized in order to protect the automobilebody from whirled-up stones as well as spray water and in order todiminish the noise level in the interior of the vehicle and on theoutside the vehicle.

[0002] When driving on gravel-paved streets and on wet roadways, stonesand/or droplets of water are carried along by the tires and propelled athigh speed against the vehicle body. On the one hand, this causes damageto the vehicle finish on the underside, so that corrosion may set in. Inaddition, the transfer of energy from the stones to the vehicle bodyleads to a broad-band, impulse-like vibration excitation (soundconducted through solids) of the vehicle body, which is radiated intothe interior of the vehicle or outside of same in form of rattling—orcrackling noise.

[0003] Hitherto customary facings of the wheel housing and theunderfloor were typically made of plastic and essentially serve only forprotecting the vehicle body from impacting stones. Due to thehard-surfaced solid construction, the vibration energy is not convertedinto heat upon the impact of the stones or water droplets, but isradiated as airborne sound either directly from the structural memberor, after transfer of solid-borne sound, from the vehicle body. Othernoises in the underfloor region, for example rolling motion noises orfume emission noises resulting from the exhaust train are reflected inundiminished fashion by the hard-surfaced facings.

[0004] A molded element of the here concerned type, serving as wheelhouse facing is known from EP-A-222 193. The layered constructioncomprises a dual layer, made of a layer of fibrous material and aplastic fiber layer. The two layers are needled together. Followingjoining by needles, the dual layer is molded by thermal deformation intoa stable shell, adapted to the contour of the wheel housing. The plasticfiber/fibrous material dual layer shell, joined by means of needles, is,overall, relatively stable or hard after its deformation, so that itcannot optimally satisfy customer demands for more efficient noisereduction.

[0005] The present invention is based on the object of designing amolded element of the initially mentioned type in such manner that thereis improved air-borne noise absorption and minimized excitation ofsolid-borne sound. In addition, the invention-specific type elementsmust be producible in simpler fashion.

[0006] According to the invention, these objects are solved by thedistinguishing characteristics of the patent claims.

[0007] The basic benefit of the multi-layer construction according tothe invention consists in that the kinetic energy of impingingprojectiles (stones, water droplets etc.) is distributed and attenuatedover a large elastic volume. The entire element achieves efficient noisereduction, while low in weight, and this applies both with respect toexcitation from projectiles as well as with respect to rolling motionnoise. Whereas with relatively hard shells, the exterior noise isreflected and again radiated, with the molded element according to theinvention it is possible substantially deposit the sound energy in theelastic-mass-system, which is formed by the relatively thick elasticlayer and the wheel-side cover layer or cover layers, so that it isdissipated therein. In addition, absorption of high-frequency soundtakes place in the top layer of fibrous material and of low-frequencysound in the total system.

[0008] In contrast to the state of the art, the manufacture of a moldedelement according to the invention is also simplified. It is no longernecessary to produce a needle-joined dual layer in a separate productionstep prior to the deformation of the element. Aside from joining anddeformation of the layer construction, it is possible in one singleworking step to also undertake local compression, for example in thearea of the edges. This results in complete sealing of the inner elasticlayer, so that hollow spaces accessible to water and mud can no longerdevelop. Delaminating of the layered construction is reliably prevented.

[0009] Further benefits and details of the invention will be explainedbased on the exemplary embodiments which are schematically representedFIGS. 1 to 12.

[0010] FIGS. 1 to 4 present variations of the layered construction of amolded or structural element 1 according to the invention. Foridentification of position, a wheel 2 is respectively indicated.

[0011] In FIGS. 1 to 4, the relatively thick elastic layer, enclosed bycover layers 4, 5 (and/or 8) is designated with 3. Layer 4, respectivelylocated on the side facing the vehicle, is a sufficiently heavy(approximately 500μ) thermoplastic or duroplastic cover layer (made forexample of polypropylene film or resin-coated PES fabric) whichcontributes not only the sealing function but also mechanical stabilityto the structural element 1 and which serves as a base for the assembly.

[0012] In the embodiment according to FIG. 1, layer 5 is provided on thewheel side. This involves, for example, a film made of thermo- orduro-plastic material, whose essential function it is to absorb anddistribute the impact energy. This film is so thin (e.g. 100μ) thatsolid-borne sound excitation does not take place by macroscopicdeformation. Local deflections in the film are spring-cushioned andattenuated by the inner elastic layer 3. In addition, said foil formsprotection for the inner layer 3 and increases dimensional stability aswell as stability of total construction.

[0013] In the embodiment according to FIG. 2, layer 5 is covered on theside facing the wheel—that is to say, it is covered with a relativelythin polyester fabric with a weight per unit area on the order of 100g/m². Said layer 6 already exercises a braking effect on stones, waterdroplets etc., so that layer 5 needs to only absorb the remaining impactenergy and distribute same over the elastic layer. Of essentialsignificance are, in addition, the absorption of high-frequency sound,the protective effect of the layer located behind and the improvedhandling of the structural element.

[0014] The inner layer 3 with a weight per unit area on the order of 300g/m² functions as spring for the vibration brought in from the previouslayer. It may be needled for improvement of elastic properties. In theembodiment according to FIG. 3, layer 8, designed as a type of coverlayer 4, has the function of layers 5, 6 according to FIG. 2.

[0015] In the exemplary embodiment according to FIG. 4, a cover layer 9is also provided on the side of structural element 1, facing away fromwheel 2. It is appropriately made of the same material as layer 6,facing the wheel. It improves the high-frequency absorption and hasproven itself appropriate for the handling of the softened foil 4.

[0016] In all types of embodiments according to FIGS. 1 to 4, the layer5 or 8, respectively facing the wheel, is designed in such manner so asto prevent acceptance of water- and/or mud.

[0017] Absorption of air-borne sound essentially takes place via theinner layer 3, which is protected from taking in water because of thecover layers.

[0018]FIG. 5 schematically depicts a molded element 1 according to theinvention designed for a wheel housing, onto the outside of which isattached a function-expanding element 10. Such locally attached andlocally effective layer segments 10 are appropriate, for example, in thearea of perforations towards the engine (schematically indicated in FIG.5 and identified with 11), or in the vicinity of the exhaust gas line.For example, a heavy foil segment can increase attenuation locally, afoil absorber is able to improve absorption and an aluminum foil canimprove heat protection. Suitable additional foil segments can, finally,also still further increase the ability to resist wear and tear and/orsimplify cleaning.

[0019]FIG. 5 also indicates that the structural element 1 is equippedwith a T-structure 12. It comprises the wheel-side extension 12 a and,vertically supported thereon, section 12 b. The purpose of theT-component 12 will be described later on.

[0020] As material for the cover layers 4, 5 and/or the textured fabrics6, 9 the following materials may be employed: polyester (PES)polypropylene, polyethylene or carbon fiber. Acoustically particularlyeffective is a cover fabric with a weight per area unit of approximately50 to approximately 200 g/m², preferably approximately 120 g/m².

[0021] With respect to the acoustical effect of the spring-mass-system,the properties of layers 3 and 5 (material, thickness) are particularlyrelevant. The following materials may be used for layer 5:polypropylene, polyethylene, polyester, polyurethane, EPDM, caoutchouc,thermo-plastic materials having similar properties—all of them new orre-cycled—or also mixtures of the named materials. They have suitablechemical properties and a relatively low weight. The thickness of layer5 ranges appropriately between 100 to 500 μm, preferably between 150 to250 μm.

[0022] As already mentioned, the cover layer 4, which is facing awayfrom the wheel 2, is made of the same material as cover layer 5. Itsthickness is greater than the thickness of cover layer 5, namely 200 to1000 μm, preferably 300 to 600 μm.

[0023] Layer 3, which, appropriately, is to have excellent elastic andabsorption properties, can be made of textured fabric or also of foam.As textured fabric materials may be employed the following: polyester,polypropylene, other thermoplastic materials having similar properties,cotton, cellulose, mineral wool or mixtures of these materials. Thetextured fabric may be designed as layers of textured fabric or asblow-type textured material. The joining technology also has aninfluence upon the desired effect. Appropriate is the use of a needledfabric, a thermo-bonding fabric or a mixture of the two.

[0024] Hardness and spring force of layer 3 are specified by

[0025] a) the titer of the employed fibers, which indicates the weightof the individual fiber and which represents a measure for the thicknessof the fiber and thus for the spring force. In actual practice,combinations of different titers are employed in order to obtain bothsoft finish (micro-fiber) as well as re-set force (bristle-type).

[0026] b) Geometry of the fibers (curling, cross-sectional distribution)

[0027] c) orientation of the fibers

[0028] d) percentage of bi-component fibers (BIKO) which produce, inthermally fused fabrics, the fusing within the fabric by melting of theone component. A BIKO percentage between 0 and 40% is typical, apercentage of 20% is preferred.

[0029] e) the titer of the BIKO fibers, which typically lies between 1and 20 dtex, preferably 6.6 dtex, but which, in extreme cases, may alsoamount to up to 120 dtex or <1 dtex.

[0030] The weight of the fabric layers lies appropriately between 200and 600 g/m², preferably approximately 300 g/m².

[0031] Foam layers which can be utilized as elastic layer 3 consist,appropriately, of polyurethane, polyethylene, EVA or thermo-/duroplasticmaterials.

[0032] Finally, a component of the resilient layer 3 may also be gas orair. Pre-requisite for said solution is that the cover layers 4 and 5form a sealed-off pocket, which envelops the layer of air. The hollowspace formed by the cover layers 4 and 5 contains, for example, a fabricor foam layer plus air. The possibility also exists that with suitablegeometry the inventive structural component 1 comprises only the twocover layers 4, 5 and a gaseous elastic layer 3. It is essential thatthe air cushion, delineated by the cover layer, possesses the necessaryresilient force.

[0033] The properties (in particular stability and effectiveness) of theinventive structural element or molded component 1 depend upon theirweight. Therefore, weight must be chosen according to application.Suitable weights range between 400 and 2000 g/m².

[0034] A molded component according to the invention can be produced,for example, of sheets in one working step. By making use of therelatively thick elastic layer, it is possible to vary the thickness ofthe structural element 1 and its local mechanical and acousticproperties by means of tooling shape and extent of extrusion. Forexample, the edges of the component 1 can be extruded in such mannerthat no hollow spaces develop, in other words, so that the inner elasticlayer 3 is totally sealed off.

[0035] The stability of the component is significantly increased by useof several layers, since the sandwich compound functions like adouble-T-support. Further increase in stability can be attained by foildistance and structuring of the component. Optimization of stability andacoustic effectiveness is only possible with the inventive moldedelement 1. A comparable mass-produced structural element, which is inaccordance with the state of the art (trilaminate) is heavier and lesseffective and clearly presents lower stability through the supportingplastic layer in the center of the construction. The thickness of themulti-layer molded component according to the invention varies betweenapproximately 1 mm (extruded) and 10 mm and ranges typically between 3and 6 mm.

[0036]FIGS. 6A and 6B reveal another variation of the component 1according to the invention as well as a method for the manufacture ofsaid components.

[0037]FIG. 6A depicts, schematically, a semifinished article 13, whichcomprises a middle layer 14 and two cover layers 15, 16 laminatedthereon. The middle layer 14 corresponds, insofar as its properties areconcerned, to the cover layers 4, 5 of an inventive molded element.Layers 15 and 16 correspond to layers 6, 9 of an inventive moldedelement.

[0038] When manufacturing molded elements 1 from semifinished articles13 of this type, the simplified handling is of benefit compared with thepurely individual materials. For example, a cover layer laminated onboth sides with fibrous material can be better heated by means ofcontact without pasting up the heating plates, and without sagging whenbeing softened.

[0039] Multi-layer molded elements 1 can be produced by folding thesemifinished item 13. The arrows in FIG. 6A indicate a folding methodwhich is completed when implemented according to FIG. 6B. In thespecific embodiment represented in FIG. 6B, the layer system of thesemifinished item 13 are placed, at a distance, above each other andform a hollow space 18. In said hollow space can be located an air layer(as represented), a fibrous material-/foam layer or a combination ofair- and fibrous material-/foam layer. These layers form a resilientlayer 3 of the structural component 1. The layer 14 forms the coverlayers 4 or 5. The two layer systems, however, need not necessarily forma hollow space after folding. They can be placed on top of each other.The two adjoining and accordingly designed cover layers 15 form theresilient layer 3 in this specific embodiment.

[0040] In FIG. 6B it is schematically indicated that the structuralcomponent 1 is compressed in its marginal area in such manner that theair located in hollow space 18 cannot escape. Designing the structuralelement 1 as an air cushion is thus possible. For manufacturing astructural element of this kind, cover layers 15, 16 are not absolutelynecessary. In this case, the inventive component consists only of an aircushion which is delimited by the cover layers 4, 5. When producing suchan air pocket, it is appropriate to employ the blow-molding method.

[0041] Shaping of inventive molded components 1 is done under employmentof pressure and/or heat. During the pressing-/cool-down step, theelastic/absorbing volume can be enlarged by inflation with air, as aresult of which there is improvement in the acoustic effect and foldformation is prevented in the foil facing the wheel. In the blow-formingmethod, a pressurized air nozzle is inserted into the resilient layer 3through a recess in the sealing edge of the press tool or a hole in thecover layer. FIG. 6B depicts a nozzle of this type, which is identifiedwith 19. The resulting aperture can subsequently be pressed together oroptionally also be used as run-off. By appropriate design of the hole(flow, cross-section) optimization of the elastic properties of thecomponent are also possible (air pump effect).

[0042] Fold formation and bulge development in the structural componentcan also be prevented by pre-stressing of the material. As a result, thepressing turns, in part, into a deep-drawing. In the extreme case, avacuum deep-drawing is also possible.

[0043] Formation of marginal regions of the inventive structuralcomponents 1 are apparent from FIGS. 7, 8, 9. Their edges are allhard-pressed. It must be prevented that these hard-pressed areas (neededfor sealing and required as edge delimitation for reasons of stability)will rub against the body of the vehicle and do damage to the appliedprotective coating, thus causing corrosion to the vehicle. Contactbetween hard-pressed edges 21 and the body of the vehicle can beprevented in different ways:

[0044] a) padding of edges by application of an isolating layer, forexample foam or caoutchouc- and/or resin mass.

[0045] b) Application of a separate protective- and/or cover strip 22,for example of rubber (piping band) FIG. 7.

[0046] c) skilful trimming of the structural component, so that layers4, 5, 6, 9 are removed outside of the hard-pressed marginal region andthe farther brought-out fibrous material 3 itself forms a cushion (FIG.8).

[0047] d) Air balloon-like cushion 23, by employing the blow-moldingmethod or by deep-drawing.

[0048] In order to render structural components of the inventive typesuitable for multiple use, it is appropriate to equip the marginalregions with T-structures of the kind represented in FIG. 5. Functionsof the T-piece are, for example, integration of spoilers foraero-dynamics or of mud flaps. Moreover, it is possible with a T-pieceto simplify attachment of the structural component to the sub-floor.Until now, it was only possible to realize such hinged segments withinjection molding components. Textile molded pieces according to thestate of the art had to be supplemented with separate (purchased) add-onparts.

[0049] FIGS. 10 to 12 indicate that T-fittings can also be realized invarious modes with multi-layer molded components according to theinvention:

[0050] a) by folding and hard-pressing of the material (FIG. 10).

[0051] b) by opening up the material and inserting additionalfoils/fibrous materials in “dovetail geometry” (FIG. 11).

[0052] c) by “pulling out” the upper foil, as a result of which it ispossible to integrate, for example, cable holders and similar functions.(FIG. 12).

1. Multi-layer element (1) suitable for bottom covering of motor vehiclefloor areas or wheel housings, characterized in that the layeredstructure comprises a resilient layer (3) enclosed by cover layers (4,5, or 8), said resilient layer (3) being designed in such manner that itforms an elastic mass system together with the most proximatelyvis-a-vis the wheel (2) arranged cover layer (5).
 2. Molded elementaccording to claim 1, characterized in that the needled resilient layer(3) preferably consists of fibrous material and weighs between 200 and400 g/m².
 3. Molded element according to claim 1, characterized in thatthe resilient layer (3) is made of foam.
 4. Molded element according toclaim 1, characterized in that the resilient layer (3) is a layer ofair.
 5. Molded element according to claim 1, characterized in thatcomponents of the resilient layer (3) are fibrous material and/or foamand/or air.
 6. Molded element according to one of claims 1 to 5,characterized in that the cover layer (5) facing the wheel consists of athermoplastic material or a material having similar properties, rangingin weight from 50 to 1000 g/m² and having a thickness from 100 to 500μm, preferably 150 to 250 μm.
 7. Molded element according to one ofclaims 1 to 6, characterized in that the cover layer (4) facing awayfrom the wheel (2) consists of a thermoplastic material or a materialhaving similar properties, ranging in weight from 150 to 1500 g/m² andhaving a thickness from 200 to 1000 μm, preferably 300 to 600 μm. 8.Molded element according to one of claims 1 to 7, characterized in thatat least one cover layer (6, 9) is provided, which is appropriatelydesigned as fibrous material with a weight per unit area of 50 to 200g/m², preferably approximately 120 g/m².
 9. Molded element according toclaim 8, characterized in that as wheel-proximate layer a layer (8) ischosen, preferably of resin-treated fibrous material, which has thefunction of the wheel-proximate layers (5, 6).
 10. Molded elementaccording to one of the preceding claims, characterized in that it isadditionally equipped with a function-expanding element (11).
 11. Moldedelement according to one of the preceding claims, characterized in that,overall, it has a weight per unit area of 400 to 2000 g/m².
 12. Moldedelement according to one of the preceding claims, characterized in thatits thickness ranges between 1 and 10 mm, preferably between 3 and 6 mm.13. Molded element according to one of the preceding claims,characterized in that the cover layers (4, 5) are laminated on bothsides with a layer of fibrous material (6, 9).
 14. Molded elementaccording to one of the preceding claims, characterized in that itsmarginal sections are directly pressed together.
 15. Molded elementaccording to one of the preceding claims, characterized in that itsedges (21) are padded.
 16. Molded element according to one of thepreceding claims, characterized in that the T-shaped structures (12) areprovided for purposes of attachment or expansion of function.
 17. Moldedelement according to claim 14, characterized in that an aperture (19) isprovided serving as run-off.
 18. Molded element according to claim 17,characterized in that the resilient layer (3) consists, at least inpart, of gas and that the aperture (19) serves for adjustment of elasticproperties.
 19. Method for producing a molded element (1) having thecharacteristics of one of Patent claims 1 to 18, characterized in thatit is manufactured, in one operating step, from supplied super-posedpaths, in that same are joined with each other by means of heat. 20.Method according to claim 19, characterized in that they are joined witheach other, deformed and locally pressed together in one tool. 21.Method for manufacturing a molded element having the characteristics ofone of Patent claims 1 to 18, characterized in that it is made byfolding a semifinished product (13), which is formed by a layer (14)having the properties of cover layers (4, 5) and that the resilientlayer (3) is inserted between the folded layers of the semifinishedproduct.
 22. Method according to claim 21, characterized in that thesemifinished product (13) is formed by a layer (14) and at least onecover layer (15, 16) having the properties of cover layers (6, 9). 23.Method according to one of the preceding claims 19 to 22, characterizedin that the blow-molding method or the deep-drawing method is employed.24. Method according to one of claims 19 to 23, characterized in thatthe edges (21) of the molded element (1) are pressed together. 25.Method according to claim 24, characterized in that the edges (21) arepadded.
 26. Method according to one of the preceding claims 19 to 25,characterized in that it is fitted with T-structures (12).